PCB testing methods during manufacturing and assembly?

I am getting a PCB manufactured for a project that I am working on. One of the parts, the A4950 motor driver, has a “pad” on the bottom, which is meant to be soldered to GND of the PCB for thermal dissipation. I was thinking about the prototyping, and I am unsure how I would go about (using a soldering iron), soldering the pad on the bottom.

I ordered PCBA for IoT device and received the hardware product with good quality. However, there is a process I ignored before – firmware development based on the hardware. How should I move on?